Cryogenic pump system

ABSTRACT

A cryogenic pump system for lifting a cryogenic fluid stored in a cryogenic tank includes a first pump assembly and a second pump assembly. The first pump assembly includes a boost pump that is configured to be disposed within the cryogenic tank and pump the cryogenic fluid received from the cryogenic tank. The second pump assembly is configured to receive the cryogenic fluid from the first pump assembly. The second pump assembly includes a housing, a stator, a reciprocating member, and at least one piston. The housing is adapted to store the cryogenic fluid received from the boost pump. The stator is adapted to produce a magnetic field. The reciprocating member is disposed within the housing and is configured to move based on the magnetic field. The piston is configured to be moved by the reciprocating member to direct the cryogenic fluid from the housing out of the cryogenic tank.

TECHNICAL FIELD

The present disclosure relates to a cryogenic pump system. More particularly, the present disclosure relates to a cryogenic pump system that is configured to lift a cryogenic fuel from a cryogenic tank.

BACKGROUND

Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) either alone or in combination with another liquid or gaseous fuel (e.g., diesel fuel). Natural gas may be more abundant and, therefore, less expensive than other liquid fuels. In addition, natural gas may bum cleaner in some applications, and produce less greenhouse gas.

Natural gas, when used in a mobile application, may be stored in a liquefied state, onboard an associated machine. This may require the natural gas to be stored at cold temperatures, typically about −100 to −162° C. Liquefied natural gas (LNG) may be drawn from a cryogenic tank by a high-pressure pump to increase a pressure of the LNG and direct the LNG to the machine's engine. A difficulty associated with pumps operating at cryogenic temperatures involves flash boiling of the natural gas due to low pressures observed commonly during retracting strokes of the pump's pistons. The problem of flash boiling may be accentuated due to heat rejected by the pump to the LNG.

United States Publication No. 2016/0281666 relates to a cryogenic pump for use with a fuel system having a tank. The pump includes an inlet configured to connect the tank to a barrel at a front side of the plunger, and an outlet connected to the barrel at the front side of the plunger. The pump may further have a vent line configured to extend from the barrel at a back side of the plunger to a location outside of the tank.

SUMMARY OF THE INVENTION

In one aspect, the disclosure is directed towards a cryogenic pump system for lifting a cryogenic fluid stored in a cryogenic tank. The cryogenic pump system includes a first pump assembly and a second pump assembly. The first pump assembly includes a boost pump that is configured to be disposed within the cryogenic tank and pump the cryogenic fluid received from the cryogenic tank. The second pump assembly is configured to receive the cryogenic fluid from the first pump assembly. The second pump assembly includes a housing, a stator, a reciprocating member, and at least one piston. The housing is adapted to store the cryogenic fluid received from the boost pump. The stator is adapted to produce a magnetic field, and the reciprocating member is disposed within the housing and is configured to move based on the magnetic field produced by the stator. The at least one piston is configured to be moved by the reciprocating member to direct the cryogenic fluid from the housing out of the cryogenic tank.

In another aspect, the disclosure relates to a cryogenic fuel system for an engine. The cryogenic fuel system includes a cryogenic tank and a first pump assembly. The cryogenic tank is configured to store a cryogenic fuel. The first pump assembly includes a boost pump that is configured to be disposed within the cryogenic tank and pump the cryogenic fluid received from the cryogenic tank. The second pump assembly is configured to receive the cryogenic fluid from the first pump assembly. The second pump assembly includes a housing, a stator, a reciprocating member, and at least one piston. The housing is adapted to store the cryogenic fluid received from the boost pump. The stator is adapted to produce a magnetic field. The reciprocating member is disposed within the housing and is configured to move based on the magnetic field produced by the stator. Further, the at least one piston is configured to be moved by the reciprocating member to direct the cryogenic fluid from the housing out of the cryogenic tank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary machine including a cryogenic tank to store a cryogenic fluid, in accordance with the concepts of the present disclosure;

FIG. 2 is a schematic representation of the cryogenic tank installed with a cryogenic pump system to lift the cryogenic fluid out of the cryogenic tank, in accordance with the concepts of the present disclosure; and

FIG. 3 is a schematic representation of the cryogenic tank having an alternate embodiment of the cryogenic pump system, in accordance with the concepts of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, a machine 100 is disclosed. The machine 100 may be a locomotive system. The machine 100 includes a locomotive 102 with an engine assembly 104 mounted on the locomotive 102. The machine 100 also includes a fuel tender 106 that is coupled with the locomotive 102. The fuel tender 106 may be arranged sequentially behind the locomotive 102 relative to a direction of machine travel (see direction, A). The fuel tender 106 may include and/or represent a storage system for a cryogenic fluid that may be applied as a fuel for powering the machine's movement over an expanse of an associated railroad.

In an embodiment, the machine 100 includes a single engine assembly 104, although it is possible to have multiple engine assemblies connected to each other to facilitate machine movement. As an example, the machine 100 may include a train propelled by the single engine assembly 104 or by multiple engine assemblies. Further, other known arrangements of locomotives may also be contemplated. A number of wheels 108 are positioned throughout a length of the machine 100 in a known manner. The wheels 108 engage tracks 110 of the railroad, supporting and facilitating traversal of the machine 100 over the railroad. Although aspects of the present disclosure are applicable to a locomotive system, aspects of the present disclosure are applicable to various other machines and environments.

The engine assembly 104 represents one of the commonly applied power generation units in locomotive systems. The engine assembly 104 includes an engine 114, such as an internal combustion engine, and a cryogenic fuel system 116 for the engine. The engine 114 may be housed within an engine compartment of the engine assembly 104, as well known. The engine 114 may be powered at least party or fully by gaseous fuel, such as liquefied natural gas (LNG). In some implementations, the engine 114 may be a high-pressure natural gas engine that is configured to receive a quantity of gas by direct injection. In general, the engine 114 may use natural gas (NG), propane gas, hydrogen gas, or any other suitable gaseous fuel, singularly or in combination with each other, to power the engine's operation. Alternatively, the engine 114 may be based on a dual-fueled engine system, a diesel-fueled engine system, or a spark ignited engine system. The engine may embody a V-type, an in-line, or a varied configuration as is conventionally known. The engine is a multi-cylinder engine, although aspects of the present disclosure are applicable to engines with a single cylinder as well. Further, the engine may be one of a two-stroke engine, a four-stroke engine, or a six-stroke engine. Although these configurations are disclosed, aspects of the present disclosure need not be limited to any particular engine type.

Referring to FIGS. 1 and 2, the cryogenic fuel system 116 facilitates a delivery of a cryogenic fuel to the engine 114, for powering the engine 114. The cryogenic fuel system 116 includes a cryogenic tank 120 (which also forms a part of the fuel tender 106) that facilitates a storage of the cryogenic fluid (i.e. a cryogenic fuel), such as LNG. In some implementations, the cryogenic tank 120 may be mounted to a base platform of the fuel tender 106, and in turn, the base platform may be supported on the railroad by the wheels 108. Furthermore, it may be noted that a usage of the term ‘cryogenic fluid’ in the present disclosure may be interchangeable with the term ‘cryogenic fuel’.

The cryogenic tank 120 may include an insulated, single or multi-walled configuration. In one example, the cryogenic tank 120 is configured to store the cryogenic fuel at relatively low temperatures. For example, the cryogenic tank 120 is configured to store the cryogenic fuel at a temperature below −160° C., in a liquid state. The cryogenic tank 120 is fluidly coupled to the engine 114 to supply the cryogenic fuel to the engine 114.

Referring to FIG. 2, the cryogenic fuel system 116 further includes a cryogenic pump system 122 that is configured to lift the cryogenic fluid out of the cryogenic tank 120 and assist with the supply of the cryogenic fluid to the engine 114. A cryogenic fluid supply from the cryogenic tank 120 to the engine 114 may be established by dedicated fuel flow passages (not shown) that may be incorporated into the machine 100, according to a general practice of the art. The cryogenic pump system 122 includes a first pump assembly 124 and a second pump assembly 126. Both the first pump assembly 124 and the second pump assembly 126 are adapted to be disposed within the cryogenic tank 120 (see FIG. 2). To this end, the cryogenic tank 120 may include an aperture 130 formed atop a roof 132 of the cryogenic tank 120 to allow an insertion and assembly of the first pump assembly 124 and the second pump assembly 126 within the cryogenic tank 120.

In some implementations, the cryogenic pump system 122 includes a support structure 134 to mount the first pump assembly 124 and the second pump assembly 126 within the cryogenic tank 120. The support structure 134 may include a cylindrical portion 128 that includes a wall 138 of the cylindrical portion 128. The support structure further includes a flange plate 142 that connects and supports the wall 138 to the roof 132 of the cryogenic tank 120. For example, the support structure 134 may be welded or bolted to the roof 132 of the cryogenic tank 120.

Details of the first pump assembly 124 will now be described. The first pump assembly 124 may be low pressure pump assembly in relation to the second pump assembly 126 that may be a high pressure pump assembly. The first pump assembly 124 includes a boost pump 144 that is configured to be disposed relatively lower in elevation to the second pump assembly 126, within the cryogenic tank 120, and below a cryogenic fuel level. In some implementations, the boost pump 144 is configured to be situated near a lower portion or a base of the cryogenic tank 120 and is coupled to and supported by the support structure 134. The boost pump 144 is configured to pump and lift the cryogenic fluid from the cryogenic tank 120 to the second pump assembly 126, and in so doing, may provide additional pressure head to suppress a flash boiling of the cryogenic fluid since suction may be periodically generated by the second pump assembly 126 (discussed later). Flash boiling of the cryogenic fluid is possible since the cryogenic fluid is susceptible to a receipt of heat from the second pump assembly 126, during operation. The first pump assembly 124 also includes a motor 146, and a motor housing 148.

The motor 146 is configured to drive the boost pump 144 by a driveshaft 150. The motor 146 may be powered by electricity sourced from a power source, such as an electric storage apparatus or from a generator of the machine 100. To supply electricity, for example, wires and/or cabling 154 may be routed into the cryogenic tank 120 from the power source, and be routed through dedicated wire conduits, defined within the cryogenic tank 120, all the way to the motor 146.

The motor housing 148 may be adapted to accommodate the motor 146. An assembly of the motor 146 within the motor housing 148 may be such that a space 156 is defined between the motor 146 and the motor housing 148. In an implementation, the motor housing 148 may be fluidly coupled to the boost pump 144, so as to receive the cryogenic fluid from the boost pump 144 via a riser 158 into the space 156. Further, the motor housing 148 may include a delivery conduit 160 to facilitate supply of the cryogenic fluid received from the boost pump 144 to the second pump assembly 126.

The boost pump 144 may work according to a centrifugal pumping principle. In some implementations, the boost pump 144 may embody vane pumps, or any other pumps that are known in the art. The boost pump 144 is a submersible pump that is submerged into the cryogenic fluid of the cryogenic tank 120, as shown. The boost pump 144 may be adapted to pump the cryogenic fluid at a relatively lower pressure than the second pump assembly 126. For example, the boost pump 144 may be adapted to pressurize the cryogenic fluid to an operating pressure of about 150 psi, and therefore the first pump assembly 124 may be configured to deliver (i.e. lift) the cryogenic fluid at a pressure of about 150 psi to the second pump assembly 126. In some implementations, both the boost pump 144 and the motor housing 148, with the motor 146 housed within the motor housing 148, is coupled to the support structure 134. The motor housing 148 and the boost pump 144 may be coupled to the support structure 134 by a bolted or a welded connection.

Optionally, the motor 146 of the boost pump 144 may be positioned outside the cryogenic tank 120 (see FIG. 3). A driveshaft 150′, similar to the driveshaft 150, may be coupled between the motor 146 and the boost pump 144, and may pass through a wall of the cryogenic tank 120, so as to transfer a motion from the motor 146 to the boost pump 144. In such an embodiment, the motor 146 may be coupled to an outside of the flange plate 142 (or an outer surface of the cryogenic tank 120) by way of one or more of a magnetic coupling and/or a dynamic sealing arrangement. In such a scenario, it may be appreciated that a cooling of the motor 146 may be attained by natural convection provided by an ambient outside environment 224. Additionally, it may be envisioned that the boost pump may be directly coupled to the housing via a direct delivery duct 162. Remaining aspects of such an embodiment may remain similar in form and function to what has been disclosed for the cryogenic pump system 122.

Details of the second pump assembly 126 will now be discussed. The second pump assembly 126 may be a high pressure pump assembly in relation to the first pump assembly 124, as already noted above. The second pump assembly 126 is configured to receive the cryogenic fluid from the boost pump 144 (i.e. from the first pump assembly 124). The second pump assembly 126 includes a linear actuator 170, a piston assembly 172, and a housing 174. The linear actuator 170 in turn includes a stator 176 and a reciprocating member 178.

The housing 174 defines an inner volume that is configured to receive and store the cryogenic fluid from the boost pump 144 (i.e. the first pump assembly 124) through the delivery conduit 160. The housing 174 may be fastened to the support structure 134, and may be disposed higher in elevation relative to the boost pump 144, as shown in FIGS. 2 and 3. The housing 174 includes a lower end 180 and an upper end 182, with at least one of the lower end 180 and the upper end 182 being coupled to the piston assembly 172 (details of the piston assembly 172 are discussed later). Openings 184, 186 may be respectively formed at the lower end 180 and the upper end 182 of the housing 174 to allow a portion of the reciprocating member 178 to extend outside the housing 174. Further, a coupling of the housing 174 to the support structure 134 may remain similar to a coupling that has been described of the boost pump 144 (or the motor housing 148) to the support structure 134. The support structure 134 stacks the boost pump 144 (i.e. the first pump assembly 124) and the second pump assembly 126 within the cryogenic tank 120 such that the second pump assembly 126 is positioned at a higher elevation than the boost pump 144 (i.e. the first pump assembly 124).

The stator 176 may be configured to produce an electrical field. The stator 176 may be disposed within the housing 174, and may extend from the upper end 182 to the lower end 180. It may be appreciated that the arrangement of the stator 176 within the housing 174 may vary, and in certain implementations, the stator 176 may be positioned with a clearance to the upper end 182 and/or the lower end 180. The stator 176 may include windings that are oriented in a vertical direction (i.e. along an elevation, E, of the cryogenic tank 120).

The stator 176 may circumferentially surround the reciprocating member 178 according to a conventional stator-rotor relationship such as in vector motors, stepper motors, etc., and which may be envisioned by those of skill in the art. The stator 176 is configured to be energized by a power supply received through the electrical cabling 154, and upon an energization, the stator 176 may produce and/or generate a magnetic field. In an embodiment, the housing 174 itself may act as a stator, and may include windings that are oriented according to an orientation suggested for the stator 176 above.

The reciprocating member 178 may be disposed within the housing 174, and surrounded by the stator 176, and may be configured to move based on the magnetic field produced by the stator 176. To this end, the reciprocating member 178 may include laminates 188 mounted on a shaft 190. Winding may be disposed on and around the laminates 188 to form alternating poles that respond to the magnetic field and cause a reciprocatory movement of the reciprocating member 178 relative to the stator 176 (see direction, B).

The piston assembly 172 may include at least one piston and at least one piston housing. The at least one piston housing may be coupled to the housing 174 (or optionally to the support structure 134), while the at least one piston may be coupled to an end of the shaft 190 of the reciprocating member 178 so as to reciprocate within the at least one piston housing. In the depicted embodiment, two piston housings—namely an upper piston housing 192 and a lower piston housing 194, having two pistons—namely an upper piston 196 and a lower piston 198, are shown. The upper piston 196 is coupled to an upper end 200 of the shaft 190 and defines an upper fluid chamber 202 within the upper piston housing 192, and the lower piston 198 is coupled to a lower end 204 of the shaft 190 and defines a lower fluid chamber 206 within the lower piston housing 194. The upper fluid chamber 202 and the lower fluid chamber 206 are in fluid communication with the housing 174 to receive the cryogenic fluid from the housing 174 respectively via an upper conduit 210 and a lower conduit 212. It may be noted that such a flow of the cryogenic fluid into the upper fluid chamber 202 and the lower fluid chamber 206 is possible owing to a suction created by the respective reciprocatory actions of the upper piston 196 and the lower piston 198 (i.e. during a retraction stroke of the pistons 196, 198). Further, a first valve 214 may be coupled to the upper conduit 210, and a second valve 216 may be coupled to the lower conduit 212. The first valve 214 and the second valve 216 may be unidirectional valves or check valves that help restrict a back flow of the cryogenic fluid from the fluid chambers 202, 206 respectively into the conduits 210, 212 during a compression of the pistons 196, 198. The first valve 214 and the second valve 216 may control a flow of the cryogenic fluid from the housing 174 respectively to the upper fluid chamber 202 and the lower fluid chamber 206.

Further, a first outlet conduit 220 and a second outlet conduit 222 may be fluidly coupled to the respective fluid chambers 202, 206 to facilitate an exit of the pressurized cryogenic fluid out of the cryogenic tank 120. In the depicted embodiment, the upper piston 196 is at an end of a compression stroke that causes the cryogenic fluid to be pushed out of the cryogenic tank 120 through the first outlet conduit 220, while the lower piston 198 is at an end of a suction stroke that causes the cryogenic fluid to be pulled into the lower fluid chamber 206 from the housing 174 by way of the second valve 216.

Although not explicitly shown, unidirectional valves (not shown) may be respectively positioned on the outlet conduits 220, 222 to prevent a back flow of the pressurized cryogenic fluid into the fluid chambers 202, 206. A type and specifications of such unidirectional valves may be contemplated and well applied by those of skill in the art.

INDUSTRIAL APPLICABILITY

During operation, as the motor 146 is powered by a supply of electricity, the motor 146 drives the boost pump 144, and in turn facilitates a lifting of the cryogenic fluid received from the cryogenic tank 120 to the housing 174. According to the embodiment shown in FIG. 2, the boost pump 144 delivers the cryogenic fluid to the motor housing 148 through the riser 158. The cryogenic fluid delivered into the motor housing 148 enables a cooling of the motor 146 by absorbing heat generated from a working of the motor 146. Effectively, the motor 146 is cooled by a discharge of the cryogenic fluid from the boost pump 144. It may be noted that a flash boiling of the cryogenic fluid within the motor housing 148 is prevented because of a sufficient pressure (or a sufficient pressure head) that is supplied by the boost pump 144. For example, 5 to 10 psi may be sufficient pressure to prevent a boiling of the LNG. A continuous electricity supply enables the boost pump 144 to further push the cryogenic fluid out of the motor housing 148 into the housing 174 through the delivery conduit 160. According to the embodiment shown in FIG. 3, the boost pump 144 delivers the cryogenic fluid directly to the housing 174 through the delivery duct 162. In this scenario, the motor 146 is disposed outside the cryogenic tank 120, and a cooling of the motor 146 is achieved by natural convection.

Further, as a supply of electricity is also provided to the stator 176, a magnetic field is generated by the stator 176 that causes the reciprocating member 178 to reciprocate (see direction, B) relative to the stator 176 (or the housing 174). In consequence, the pistons 196, 198 move relative to the piston housings 192, 194 (i.e. the upper piston 196 relative to the upper piston housing 192 and the lower piston 198 relative to the lower piston housing 194). As a result, the cryogenic fluid stored within the housing 174 is selectively pulled into the fluid chambers 202, 206 respectively through the upper conduit 210 and lower conduit 212 (during a suction stroke of the pistons 196, 198) and then pushed out from the fluid chambers 202, 206 into the first outlet conduit 220 and the second outlet conduit 222 (during a compression stroke of the pistons 196, 198).

Heat generated by the second pump assembly 126, from electrical resistance in the stator 176 or from friction in the piston housings 192, 194 may be absorbed by the cryogenic fluid. This heat is carried away from the second pump assembly 126 by the cryogenic fluid exiting through outlet conduits 220, 222. In this manner, the second pump assembly 126 is configured to be cooled by the cryogenic fluid stored within the housing 174. It may be noted that a boil-off or a flash boiling of the cryogenic fluid due to a loss of pressure encountered during a suction stroke of the pistons 196, 198, and a temperature rise of the cryogenic fluid from an absorption of heat from the second pump assembly 126 is prevented because of the pressure head provided by the boost pump 144.

By positioning the boost pump 144 (first pump assembly 124) under the second pump assembly 126, a simplified packaging and installation of the cryogenic pump system 122 is possible. This is because both the first pump assembly 124 and the second pump assembly 126 may be inserted through the same aperture 130. For example, during an assembly of the cryogenic pump system 122 within the cryogenic tank 120, the first pump assembly 124 and the second pump assembly 126 may be first assembled with the support structure 134. Thereafter, an assembly of the first pump assembly 124 and the second pump assembly 126, together with the support structure 134, may be inserted into the cryogenic tank 120, as a single unit. Further, during a disassembly of the cryogenic pump system 122 from the cryogenic tank 120, the assembly of the first pump assembly 124 and the second pump assembly 126, together with the support structure 134, may be removed from the cryogenic tank 120 as a single unit. Further, the configuration of having the low pressure, boost pump 144 positioned upstream to the second pump assembly 126 supports the use of filter that may filter the cryogenic fluid before the cryogenic fluid is delivered to the piston housings 192, 194, which may be intolerant of debris. Moreover, the lowered position of the boost pump 144 (first pump assembly 124) in the cryogenic tank 120 may allow the boost pump 144 to attain a volumetric efficiency of 1 by overcoming pressure losses at an entrance (not shown) of the piston housings 192, 194. Additionally, there may be a provision that enables the boost pump 144 (first pump assembly 124) to bypass the second pump assembly 126 so as to supply relatively low fuel pressure applicable to other gaseous fueled engine technologies.

It should be understood that the above description is intended for illustrative purposes only and is not intended to limit the scope of the present disclosure. Thus, one skilled in the art will appreciate that other aspects of the disclosure may be obtained from a study of the drawings, the disclosure, and the appended claims. 

What is claimed is:
 1. A cryogenic pump system for lifting a cryogenic fluid stored in a cryogenic tank, the cryogenic pump system comprising: a first pump assembly including a boost pump that is configured to be disposed within the cryogenic tank and pump the cryogenic fluid received from the cryogenic tank; and a second pump assembly configured to receive the cryogenic fluid from the first pump assembly, the second pump assembly including: a housing to store the cryogenic fluid received from the boost pump; a stator to produce a magnetic field; and a reciprocating member disposed within the housing and configured to move based on the magnetic field produced by the stator; and at least one piston configured to be moved by the reciprocating member to direct the cryogenic fluid from the housing out of the cryogenic tank.
 2. The cryogenic pump system of claim 1, wherein the boost pump is driven by a motor, the motor being cooled by a discharge of the cryogenic fluid from the boost pump.
 3. The cryogenic pump system of claim 1, wherein the first pump assembly is configured to be submerged within the cryogenic fluid.
 4. The cryogenic pump system of claim 1, wherein the first pump assembly is a low pressure pump assembly and the second pump assembly is a high pressure pump assembly.
 5. The cryogenic pump system of claim 1, wherein the second pump assembly is configured to be disposed within the cryogenic tank.
 6. The cryogenic pump system of claim 1, further including a support structure to mount the first pump assembly and the second pump assembly within the cryogenic tank.
 7. The cryogenic pump system of claim 6, wherein the support structure is configured to stack the first pump assembly and the second pump assembly within the cryogenic tank such that the second pump assembly is positioned at a higher elevation than the first pump assembly.
 8. The cryogenic pump system of claim 1, wherein the second pump assembly is configured to be cooled by the cryogenic fluid stored within the housing.
 9. The cryogenic pump system of claim 1, wherein the boost pump is configured to provide the cryogenic fluid to the housing at a pressure to prevent a flash boiling of the cryogenic fluid in the housing.
 10. The cryogenic pump system of claim 1, wherein the cryogenic fluid is liquefied natural gas.
 11. A cryogenic fuel system for an engine, the cryogenic fuel system comprising: a cryogenic tank to store a cryogenic fuel; a first pump assembly including a boost pump that is configured to be disposed within the cryogenic tank and pump the cryogenic fluid received from the cryogenic tank; and a second pump assembly configured to receive the cryogenic fluid from the first pump assembly, the second pump assembly including: a housing to store the cryogenic fluid received from the boost pump; a stator to produce a magnetic field; and a reciprocating member disposed within the housing and configured to move based on the magnetic field produced by the stator; and at least one piston configured to be moved by the reciprocating member to direct the cryogenic fluid from the housing out of the cryogenic tank.
 12. The cryogenic fuel system of claim 11, wherein the boost pump is driven by a motor, the motor being cooled by a discharge of the cryogenic fuel from the boost pump.
 13. The cryogenic fuel system of claim 11, wherein the first pump assembly is configured to be submerged within the cryogenic fuel.
 14. The cryogenic fuel system of claim 11, wherein the first pump assembly is a low pressure pump assembly and the second pump assembly is a high pressure pump assembly.
 15. The cryogenic fuel system of claim 11, wherein the second pump assembly is configured to be disposed within the cryogenic tank.
 16. The cryogenic fuel system of claim 11, further including a support structure to mount the first pump assembly and the second pump assembly within the cryogenic tank.
 17. The cryogenic fuel system of claim 16, wherein the support structure is configured to stack the first pump assembly and the second pump assembly within the cryogenic tank such that the second pump assembly is positioned at a higher elevation than the first pump assembly.
 18. The cryogenic fuel system of claim 11, wherein the second pump assembly is configured to be cooled by the cryogenic fluid stored within the housing.
 19. The cryogenic fuel system of claim 11, wherein the boost pump is configured to provide the cryogenic fuel to the housing at a pressure to prevent a flash boiling of the cryogenic fuel in the housing.
 20. The cryogenic fuel system of claim 11, wherein the cryogenic fuel is liquefied natural gas. 